Elections would be contentious between Democrats and Republicans in a state where voter demographics are rapidly changing and raising the stakes for both parties, NBC News reported

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In this April 26, 2017 file photo, Sen. John McCain departs the U.S. Capitol for a briefing on North Korea at the White House in Washington, DC.

After Sen. John McCain's brain cancer diagnosis, the six-term Arizona senator declared he would "be back soon" to attend to his duties in the legislative branch — but the political ramifications of his exit could be substantial, NBC News reported.

According to Arizona law, the state governor would appoint a member of the same party to fill a Senate vacancy until the next regularly scheduled general election, which would be in November 2018.

If McCain left the Senate seat vacant before the midterm elections, Arizona would have two Senate elections in 2018 — an extremely rare event.

Elections would be contentious between Democrats and Republicans in a state where voter demographics are rapidly changing — raising the stakes for both parties.